This invention relates to a universal joint and more particularly a tripot universal joint.
Tripot universal joints are typically employed in automotive axial driveshafts and especially in front-wheel-drive vehicles between the transaxial differential and the driving wheel. The telescopic constant velocity joint such as the tripot should not only transmit the torque at various speeds, angles and telescopic positions but also prevent any vibrations of the engine from being transmitted through the joint and driveshaft to the driving wheel and the vehicle structure. In addition, when the universal joint operates at an angle it should not produce any oscillating axial excitation which may be capable of initiating vibrations in the driveshaft or in the structure of the vehicle.
U.S. Pat. No. 3,125,870 granted to Michael Orain, Mar. 24, 1964, discloses a conventional telescopic type tripot universal joint of the prior art, which has one of the best stroking type universal joints available for osculating engine vibrations from the rest of the vehicle. However, these conventional prior art tripot universal joints due to their operating friction characteristics produce internally generated osculating axial forces which are related to the transmitted torque angles. During severe accelerations at low vehicle speeds these cyclic axial forces can be of sufficient magnitude to produce a shudder type disturbance which has a frequency equal to three times the shaft speed.
To reduce this shudder or vehicle ride disturbance, the generated axial forces must be reduced. This reduction is accomplished by tracking an outer ball or ball assembly of the tripot universal joint relative an axis of the housing. Effective tracking of the outer ball to reduce shudder must have a housing ball bore designed to minimize the outer or ball assemble tip and/or reduce binding of the ball within the track when it does tip. However, ball tip occurs about two axes, the X-axis and Z-axis. The problem with previous designs is the effectiveness at preventing ball tip about the x-axis. The inability to prevent ball tip results in increased generated axial forces which lead to shudder.
A telescopic universal joint comprises a first drive member having a first longitudinal axis engaged flexibly to a second drive member having a second longitudinal axis. The first and second longitudinal axis are co-linear to one another, or zero degreed, when the joint is not flexed. The first drive member defining three longitudinal drive channels spaced circumferentially from another. Each channel has two opposing concave side surfaces spaced circumferentially apart by a back surface facing radially inward. Three trunnions of the second drive member are disposed respectively within the three channels. Each trunnion has a radial axis all lying within an imaginary plane and intersecting at a spider center lying along the second longitudinal axis.
Rotating and wobbling about each trunnion and generally about a Z-axis is a ball assembly having an outer ball which is in rolling contact with one of the two opposing concave side surfaces of the first member. The perceived wobble of the ball assembly is created by the assembly pivoting about a Y-axis disposed parallel to the channel, and pivoting about an X-axis disposed laterally to the channel, or and axis lying within the X-Y plane. Pivoting of the ball assembly about the X-axis is restricted by a central guide rail projecting radially inward from the back surface of the channel and extending longitudinally lengthwise along the channel. The ball assembly ceases to pivot about the X-axis when a radial side wall of the outer ball contacts the guide rail. By limiting this pivoting action, binding of the ball assembly against the side surfaces of the channel is minimized by redistributing the forces which would otherwise concentrate against the side surfaces.
An advantage of the present invention is the reduction of outer ball binding with the channel by eliminating contact between the tread face of the outer ball and the unloaded side surface of the channel regardless of universal joint angle.
Yet another advantage of the present invention is the reduction of universal joint shudder.